Hyperlocal Effects From A Changing Climate

Aug 06, 2010 By Phillip F. Schewe

Cities are made chiefly of concrete and asphalt, which soak up more sunlight during the day than soil and have a harder time radiating the heat away during the night. Add to that all the energy -- natural gas, electricity, gasoline -- used in high-density places, and cities become hot islands floating in a sea of cooler countryside.

On some days London is as much as 20 degrees Fahrenheit warmer than its surroundings. And that’s just because of the "urban heat island" effect. Any long-term climate effects brought on by general greenhouse warming would add additional heat.

A new study by three scientists at the Met Office, the British government agency responsible for making weather forecasts, looks at how hot cities could be by the year 2050. They use computers to predict how temperatures will change for places around the world under various scenarios, such as a doubling of the amount of heat-trapping atmospheric carbon dioxide over 1950 levels.

The urban heat island effect will only get more important in coming years since more people are moving to cities. The urban population of the world could double by the year 2050.

“The cumulative impact of climate change and continued urbanization will exacerbate the urban heat island effect in many locations,” said Mark McCarthy, one of the authors of the study, which appears in the journal Geophysical Research Letters. “This should increase the number and severity of extreme temperature events that urban citizens could be exposed to.”

If carbon dioxide is twice the 1950 levels, the Met Office simulations suggest that some cities in the Middle East could see temperature rises of 5.4 degrees while cities in the western United States, southern Asia, and western Africa would suffer an increase of about 2 degrees.

As temperatures rise, so will energy demands. When it gets hot, people turn on air conditioners, the largest consumers of electricity on a hot day. This works to cool specific rooms, but air conditioners also produce heat by removing it from indoor areas and dumping it into the wider city environment -- contributing to making hot places even hotter.

On July 19, Department of Energy Secretary Steven Chu announced action to mitigate one cause of urban heat, namely the heating of buildings by summertime sunshine. The DOE plan provides tips on to make buildings cooler by giving them light-colored roofs.

A dark roof absorbs much of the sunlight falling on it. Not only does this roof get hot, raising the surrounding air temperature, but it makes the building warmer too, which in turn calls for more air conditioning and consumes more electric power at just the time in the late afternoon when the power grid is generally stressed to its maximum load of the day. When more electricity is needed during these peak hours, generators have to work harder, and this usually means the burning of extra fossil fuel -- adding carbon dioxide and still more heat to the atmosphere.

A roof painted white, by contrast, reflects much more of the sunlight back into the sky, keeping the building beneath cooler.

“Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change,” said Chu. The DOE will begin converting its own buildings to the cool- roof protocol, and is encouraging other federal departments to use light-colored roofs too.

Roofs and pavement cover up to two-thirds of an urban area, and a recent study in the journal Environmental Research Letters by DOE’s Lawrence Berkeley National Laboratory estimated that if all cities with populations larger than one million increased their reflectivity -- the fraction of incident sunlight sent back into the sky -- by using white or silvery coatings on rooftops and parking lots, then a one-time reduction in carbon dioxide emissions of up to 57 billion metric tons could be attained.

University of California, Berkeley, professor emeritus of physics and a California energy commissioner Arthur Rosenfeld tried to put this CO2 saving in perspective.

"If we assume that roofs have a service life of 20 years, we can think of an equivalent rate of 1.2 billion metric tons per year. That offsets the emissions of roughly 300 million cars for 20 years," said Rosenfeld.

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User comments : 10

Up until the present, the (so-called) Climate Scientists have consistently failed to factor this well known and documented Urban Heat Island effect into their models. They have used the higher Urban temps w/o regard to the lower rural temps.

Of course, we know these models are fatally flawed (Mann's, hoakey er, hockey stick, no maunder minimum, no medieval warm period), but perhaps, this study will encourage these very political "scientists" to continue adding new data points until they actually move from handwavium to hard science.

CO2 is capable of producing only 1 more degree heating; its greenhouse effect is asymptotic. It is the unproven multiplier effect which would push temps higher. But the humidity increase necessary to fulfill the IPCC runaway warming theory is going ... down. Humidity is dropping at altitude. The increased temperatures at altitude, predicted along with the increased humidity at altitude is missing, too. In fact, all predictions of the IPCC have failed. Something is very wrong with the global warming theory.

Besides, cities have a rampant heating effect already, and we hardly notice it. If heat were an actual problem, we'd have to do something to cool our cities. But it is not, and we don't. So cool your jets. Now get off my lawn, punk.

3432682: You said: "Humidity is dropping at altitude. The increased temperatures at altitude, predicted along with the increased humidity at altitude is missing, too. In fact, all predictions of the IPCC have failed. Something is very wrong with the global warming theory." Of course you do nothing to show these effects (much as Shootist). In fact, the humidity is following the temperature just as it always has and just as predicted by models. In Shootist's case, he is just wrong about the models not including the heat island effects. In fact, he is about 10 years behind. For the past decade, the heat island effect has been present in both the model and the measurements. There have been, at least, three studies that all looked at the heat island effects over the past decade. They all show that the corrections for the effect accurately reflect real temperatures. To say they are not taken into effect is disingenuous.

Interesting, and explanatory, that the anti-global-warming snipers gleefully accept any science they can twist to their ends, and reject similarly peer-reviewed science that they can't think of a way to misinterpret.

Then they make sweeping generalization, unsupported by any evidence accepted by the same scientific community they selectively quote, and expect head-nodding acceptance from the awed audience.

What we're seeing is the rise of BS artists, not scientists, and they're no more believable than a little boy alibi-ing that a monster ate the cookies.

In a recent paper, the UHI effect world wide was estimated to have raised the temperature by about 0.05 deg C. The problem is the fact that measuring stations that were previously well located in rural locations now are contaminated by urban sprawl. This can give the impression of warming more than actually is happening. This is made worse by many high latitude stations being close and "estimates" being used as infill (if the cities are warming, so must the ice??!).As the UHI effect can be as high as 2 to 10 deg on some days and the models (I think) use the figure of 0.5 deg, the bias is obvious.So, the UHI effect does not add to Global temperatures, it just makes it easier for warmists to con us.

Occam's razor. Option one: Humans are contributing to climate change. Option two: Thousands of scientists have joined a conspiracy that crosses geo-political and cultural boundaries with the purpose of manufacturing a non-existent problem with dual intention of negatively affecting global business and obtaining funding to continue research this completely fictitious crisis. But then again, a high school dropout talking head on TV yelled some bumper sticker slogans at me, so the second option must be true. A meteor won't kill off the human race and neither with political correctness, rapid anti-intellectualism and our embrace of cognitive dissonance will.

patnclaire

I like the painting the rooftops white idea. But, what does this do to energy use in the /winter/? Won't this reduced heat absorption trigger more heater use in the winter? Maybe there's some regional, temperature average threshold that should be used where some (northern) cities paint their roofs black and more southern cities paint them white? Maybe a temperature sensitive paint that changes colors based on the ambient temperature? I have no idea how much that would cost though nor how much more (or less) CO2 the production of that paint would produce.

Another thing to consider... A building's surface area is composed of much more than just the roof. In many buildings, the roof is the smallest, exposed surface. Wouldn't painting the entire exterior improve this even more?

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